The integration is fine, but it's not perfect. It kicks my wife off her iPhone Hotspot every time she closes the lid on her laptop. It also burns the battery on her iPhone, which is a concern in the exact situation you'd want cellular connection (places with no wifi often don't have outlets either).

Anecdotally, I've also seen her get issues when going from an area with bad connection to an area with good connection (iPhone will disconnect).

The experience with a non-iphone is also not seamless, though that's to be expected.

Point being that reliable and easy cellular access on a MacBook would be a pretty nice improvement. This is especially true given how much of what people do on computers relies on the internet these days.